1. Topics: 1.Regulation of the Calvin Cycle 2.Photorespiration 3.CO2 concentrating mechanisms 4.Sucrose and starch synthesis

2. Regulation of the Calvin cycle a.RuBP “activase” b.Light induction of Calvin cycle gene expression c.Enzyme activites regulated by redox state of the chloroplast

3. c: Redox state of stroma: The Ferredoxin-Thioredoxin System NADPH

4. Topics: 1.Regulation of the Calvin Cycle 2.Photorespiration 3.CO2 concentrating mechanisms 4.Sucrose and starch synthesis

5. RUBISCO has a higher affinity for CO 2 compared to O 2 (lower K m ) Rubisco : K m (CO 2 )= 15 μM K m (O 2 )= 550 μ M But concentration of O 2 is much higher: Atmophere: 20% O 2 and only 0.03% CO 2 In solution: CO 2 = 12 μ M, O 2 = 265 μ M NET RESULT: a lot of O 2 gets “fixed” instead of CO 2 This process is called photorespiration. “The Problem with Oxygen”: RUBISCO reacts with oxygen as well as CO 2 (oxygenase/carboxylase)

6. RuBis Carboxylase/Oxygenase

7. P-Glycolate (C2) Glycolate (C2) Glycine (C2-N) Serine (C3-N) Hydroxypyruvate (C3) Glycerate (C3) 3-P-Glycerate (C3) Calvin Cycle Glycine (C2-N)CO2 Rib15bisP (C5) + O2 Glycolate (C2) Serine (C3-N) Glycerate (C3) NH4 Glycolate (C2) O2 H2O2 Chl. Per. Mit ATP 3xATP 2x NADPH ATP Fd

8. The cost of photorespiration 3x O 2 needs 2x ATP and 2x Ferredoxin AND high temperature increases photorespiration: *Modifies Rubisco’s kinetics: oxygenation more favorable *Decreases the CO 2 /O 2 ratio in solution

9. What do plants do?

10. CO 2 Concentrating Mechanisms a)CO 2 and HCO 3 - Pumps: aquatic organisms b)CO 2 concentrating mechanisms: higher plants

11. CO 2 Concentrating Mechanisms Clicker question: Is there only one type of CO2 concentrating mechanisms in higher plants? A. Yes B. No, there are two. C. N, there are many

12. CO 2 Concentrating Mechanisms Clicker question: Did these different mechanisms evolved from one common ancestor? A. Yes, modifications occurred later. B. No, there are two independent origins. C. No, there were many independent origins. CO2 concentrating mechanisms evolved many times independently: Convergent evolution

13. CO 2 Concentrating Mechanisms PEP-Carboxylase CH 2 II C-OPO 3 2- + HCO 3 - I COO - I CH 2 + HPO 4 2- I C=O I COO - a)CO 2 and HCO 3 - Pumps: aquatic organisms b)CO 2 concentrating mechanisms: higher plants Phosphoenolpyruvate Oxaloacetate

14. Could plants just use PEP-carboxylase instead of Rubisco?

15. C3 + HCO 3 - C4 C3 + CO 2 HCO 3 - CO 2 RUBISCO C3 Fixation/carboxylation C4 transport Decarboxylation C3-”recycling” Principles of CO2 concentration mechanisms

16. C3 + HCO 3 - C4 C3 + CO 2 HCO 3 - CO 2 RUBISCO C3 Fixation/carboxylation C4 transport Decarboxylation C3-”recycling”

17. CO 2 Concentrating Mechanisms a)C 4 Photosynthesis: spacial separation b)Crassulacean Acid Metabolism (CAM): temporal separation

18. The C4 carbon cycle: Spatial separation a.Different Cells: Bundle Sheath cells/ Kranz anatomy b.Within one cell

19. Kranz (=Wreath) Anatomy Bundle sheath cells

20. (V Single Cell C4 Photosynthesis Borszczowia

21. CAM: temporal separation Minimizing water loss H20 loss/CO2 gained (g) CAM 50-100g C4250-300g C3 400-500g

22. CAM: Day/Night switch

23. Topics: 1.Regulation of the Calvin Cycle 2.Photorespiration 3.CO2 concentrating mechanisms 4.Sucrose and starch synthesis

24. UDP-Glucose

25. Triose-P Glc-1-P Glc-NtDP NTP (ATP/UTP) PPi S a c c h a ri d e s Saccharide Synthesis: Overview Pi

26. Plastids: Starch Synthesis

27. Remember: Cellulose =  -D-1,4-glucosyl Starch is a branched polymer

28. Regulation of starch and sucrose biosynthesis

29. Triose-P Fru-1,6-bisP Fru-6-P Glc-6-P Glc-1-P UDP-Glc Suc-6-P Pi PPi ATP ADP PPi UTP Pi Sucrose SPS Phosphate is generated in the cytosol during sucrose synthesis

30. Cytosol Plastid Triose-P Pi Sucrose Synthesis Starch Synthesis Balance: Starch vs Sucrose Synthesis

31. Regulation of Starch and Sucrose Synthesis UDP-Glc + Fru-6-PSuc-6P Sucrose-P Synthase (SPS) Glc-6-P SPS-P SPS Pi Glc-1-P ADP-Glc ATP PPi 2xPi Pi 3PGA Ferredoxin Red. ADP-Glc Pyrophosphorylase (AGPase)